I have figured out exactly what I did that was wrong. What JRowan told me was correct. In order to get the directory of my device's Download folder, then I need to use this piece of code:
Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
Initially, it didn't work because I forgot to add this permission to my Android manifest:
android.permission.WRITE_EXTERNAL_STORAGE
So, to summarize, I forgot to write this crucial permission. Without it, the directory actually gets me to: /storage/emulated/0/download (which isn't what I want obviously).
Thanks to the two people who tried to answer my question!